A. Field of the Invention
The present invention is directed toward the field of manufacturing integrated circuits.
B. Description of the Related Art
Deposited tungsten nitride has the potential for being conformal and providing good step coverage. Tungsten nitride also serves as an excellent barrier to the diffusion of many metals that are used in integrated circuit metalization processes. Further, the resistivity of tungsten nitride is low in comparison to other metal barriers, such as titanium nitride. Accordingly, it is desirable to use tungsten nitride in several integrated circuit manufacturing applications. Applications in which tungsten nitride is desirable to employ include the formation of diffusion barriers, gate electrodes, and capacitor electrodes.
However, traditional processes for depositing tungsten nitride by ammonia reduction chemistry create an unacceptably large number of contaminant particles. When tungsten nitride is being deposited onto a wafer using such traditional deposition processes, the large number of particles causes an unacceptably high number of the dice on the wafer to be defective. In the integrated circuit fabrication industry, it is ideal for 30 or less contaminant particles, each having a diameter of 0.2 microns (".mu.m") or greater, to be generated from a deposition process step that is performed on an eight inch wafer. A traditional deposition of tungsten nitride on an eight inch wafer results in 90 to 300 0.2 .mu.m or greater diameter contaminant particles being generated.
Ideally, all of the contaminant particles that are generated during a deposition process are exhausted from the chamber that is employed for the deposition. However, a portion of the particles do not get exhausted. Instead, they accumulate on the inner component surfaces of the deposition chamber. Each time the deposition chamber is used, more contaminant particles accumulate on the chamber's interior.
Eventually, particles that are attached to the interior of the chamber detach and fall onto a wafer that is being processed in the chamber. When a detached particle falls onto a die on the wafer, the integrated circuit being formed on that die is contaminated and rendered defective. Increased accumulation of contaminant particles on the deposition chamber's interior results in an increase in the number of defective die per wafer being processed in the chamber.
In order to avoid an increased number of die defects, the chamber's owner must increase the frequency with which the walls of the deposition chamber are cleaned. This increases the production costs of the deposition chamber's owner. Accordingly, it is desirable to have a tungsten nitride deposition process that generates less contaminant particles than traditional tungsten nitride deposition processes.
Traditionally, the deposition of tungsten nitride is achieved by flowing a gaseous mixture including tungsten hexafluoride (WF.sub.6) and ammonia (NH.sub.3) into a deposition chamber. The chamber contains a wafer onto which the tungsten nitride is to be deposited. The tungsten hexafluoride and ammonia immediately begin to undergo a gas phase reaction to form tungsten nitride. A thermal reaction occurs to combine the nitrogen from the ammonia and the tungsten from the tungsten hexafluoride to form tungsten nitride (W.sub.2 N).
The above described traditional process for depositing tungsten nitride also results in the formation of contaminant particles in the form of solid byproducts. Several different byproducts have been observed. These byproducts include ammonia adducts of tungsten hexafluoride ((NH.sub.3) .sub.4 WF.sub.6), ammonium fluoride (NH.sub.4 F) and other ammonium complexes. A range of 90 to 300 of these solid byproduct particles having a diameter of 0.2 .mu.m or greater are generated each time tungsten hexafluoride and ammonia are combined in a traditional process to deposit tungsten nitride on an eight inch wafer. Many of these particles become attached to the deposition chamber's interior and eventually cause an increase in the number of defective dice produced by the chamber.
Further, the tungsten nitride that is deposited using the above described traditional process has a polycrystalline structure in which there are many grain boundaries. As a result, the diffusion barrier properties of the tungsten nitride are compromised.
It is desirable to have a process for depositing tungsten nitride that produces less than 90 to 300 contaminant particles per eight inch wafer. Such a deposition process would allow more dice on a wafer to be produced without defects and the frequency of chamber cleaning to be reduced. It is also desirable for a deposition process for tungsten nitride to provide for a layer of tungsten nitride that is more amorphous than traditionally deposited tungsten nitride. As a result, the diffusion barrier characteristics of the tungsten nitride layer will be enhanced over traditionally deposited tungsten nitride.